Secured document, system for manufacturing same and system for reading this document

ABSTRACT

A document includes at least one drawing or data produced, for example, by printing. In addition, this document includes a hologram representing part of the document. The hologram of this document is recorded using a system including a prerecorded or electrically controllable optical modulator in which the image of at least part of the document is recorded. This modulator is designed to be combined with a layer of photosensitive material. A first reference wave illuminates the layer of photosensitive material. A second wave incident on the modulator and giving rise to a third object wave is also transmitted to the layer of photosensitive material in order to interfere with the reference wave in this layer.

The invention relates to a secured document, a process and a systemmaking it possible to manufacture this document and means making itpossible to read it.

It is now relatively easy for forgers to reproduce conventionaldocuments such as passports, identity card, identification badges.

The object of the invention is to make it difficult, or even virtuallyimpossible, to reproduce and/or falsify such documents.

Securing documents (identity cards, passports, etc.) againstcounterfeiting and falsification is a fundamental problem which ariseswith all those involved in the field.

The restrictions which bear on the securing methods are stringent. Thisis because these documents must be made with:

-   -   a very low production cost (a few tens of centimes per document)    -   a short duration for the process allowed for the manufacture of        each document (a few seconds per document)    -   a high level of protection against counterfeiting.

Generally, the object of the invention is to produce, on the document tobe protected, a characteristic hologram which is difficult to copy andmoreover which carries printed data in a conventional manner on thedocument. Thus a verifying agent will be able to check the document bycomparing the content of the hologram with the content of the rest ofthe document. For example, the hologram represents an image of theidentity photo contained on the document. Comparing the image of thehologram with the image of the photo makes it possible to authenticatethe document quickly and easily.

The invention therefore relates to a document comprising at least onedrawing or data, made by deposition or inclusion of pigments and/or dyeswhich can be read optically, characterized in that it also comprises ahologram containing a copy of said drawing or said data.

The invention also relates to a document security system, characterizedin that it comprises a prerecorded or electrically controllable opticalmodulator in which the image of at least part of the document isrecorded, said modulator being designed to be combined with a layer ofphotosensitive material, at least one first light source making itpossible to transmit a first reference wave to the layer ofphotosensitive material and a second incident wave onto said modulatorand giving rise to a third object wave which is transmitted to the layerof photosensitive material in order to interfere with the reference wavein this layer.

The invention also relates to a system for reading a document comprisinga hologram containing an image of part of said document, said imagebeing scrambled, characterized in that it comprises a device forcorrecting said scramblings, or revealer, said hologram being readablethrough the revealer.

The various objects and characteristics of the invention will becomemore clearly apparent in the following description given by way ofexample and in the appended figures which represent:

FIGS. 1 a and 1 b, examples of documents secured according to theinvention;

FIGS. 2 to 4 c, examples of hologram recording systems according to theinvention;

FIGS. 5 and 6, recording systems making it possible to inducescramblings in the images recorded in the holograms;

FIGS. 7 and 8, systems making it possible to read a hologram by removingscramblings contained in the hologram;

FIGS. 9 and 10, a device for reading a document furnished with ahologram and making it possible to remove scramblings induced in thehologram;

FIGS. 11 and 12, documents incorporating special gratings placed againstthe holograms.

An example of a document secured according to the invention will firstof all be described with reference to FIG. 1 a. By way of example, FIG.1 shows an identity card 1 comprising data 4 indicating the identity ofthe possessor of the card, his or her photograph 2 and his or hersignature 5. Furthermore, according to the invention, the card comprisesa hologram 3 in which one or more elements for personalizing the cardhave, inter alia, been recorded, such as the photograph, the signature,etc. In FIG. 1, the photograph has been chosen for recording in thehologram. A card of this type would thus be more difficult to falsifysince the hologram contains data for personalizing the card, which willchange from one card to another.

FIG. 1 b shows a variant embodiment of FIG. 1 a. According to thisvariant the hologram 3 contains images which appear in different planes.An image 60 may be, for example in the case of an identity card, a copyof the identity group 2, whilst another image 61 may be either astandard image (logo) or other data from the card such as the copy ofthe signature 5. According to another variant (not shown), the hologrammay also comprise data printed on its surface.

A first example of the process of recording the hologram will now bedescribed with reference to FIG. 2.

A support element 22 is coated on one of its faces with a layer ofphotosensitive material 21. An optical modulator 23, such as atransparent photographic support or a controllable modulator such as aliquid-crystal screen, is applied near to or in contact with the layerof photosensitive material.

Preferably, the modulator makes it possible to supply the contents (dataor image) of part of the document to be secured. If this involves aprerecorded modulator of the transparency type, this part of thedocument is recorded in the modulator. If this involves a controllablemodulator, the part of the document can be displayed using the controlof the modulator.

The support element 22 is transparent at the recording wavelength. Amirror 24 is placed on the side opposite the photosensitive layer withrespect to the modulator 23. A light beam R supplied by a source S1 andcarrying a coherent wave illuminates the support element 22. By way ofexample, in FIG. 2, this light beam is perpendicular to the plane of thesupport element 22 and of the photosensitive layer 21. The beam R passesthrough the support 22, the holography layer 21. It is modulated by themodulator 23 and is transmitted to the mirror 24. The latter reflectsthe modulated beam which passes back through the modulator. According tothis embodiment, the mirror 24 is perpendicular to the direction of thebeam and reflects a beam collinearly with the incident beam. Thereflected modulated beam interferes with the beam R in the layer ofphotosensitive material. The modulation carried by the modulated beam istherefore recorded in the photosensitive layer. Thus, a hologramcontaining data or an image, which is a copy of data or of an imagecontained in the document to be secured, has been recorded. If themodulator 23 contains, for example, the photograph of the possessor ofthe identity card, this photo has therefore been recorded in thehologram.

In this process, it is assumed that T is the transmission coefficient ofthe modulator and that O is the wave illuminating the hologram on theside opposite the beam R, which we will call a reference wave Rhereinafter.

The function recorded by the hologram comes from the interferencebetween the reference wave R and the wave O=R.T. the object wave fromthe transparency.

The hologram records R.R.T.

If the hologram is thick, it will rediffract on reading the recordedimage, for specified angles of incidence (Bragg effect) of theillumination wave and of the viewing direction.

The modulator can integrate a scattering function for improved readingof the hologram and in order to complicate any counterfeiting.

FIG. 3 shows another recording process in which two waves illuminatingthe photosensitive layer are needed. The light modulator 23 is placedagainst the layer of photosensitive material 21 borne by the support 22.

An illuminating reference wave R supplied by the source S1 istransmitted to the layer of photosensitive material 21 without passingthrough the modulator. An illumination wave I supplied by the source S2illuminates the modulator 23 and is transmitted therethrough to thelayer of photosensitive material (illumination wave O, O=IT). The twowaves R and O interfere in the photosensitive material 21.

Preferably, the two waves O and R are counterpropagating and areperpendicular to the plane of the layer of photosensitive material 21.Also, preferably, the two waves are coherent plane waves.

The function recorded by the hologram comes from interference between R,reference wave, and the object wave coming from the modulatorilluminated by the plane wave I: O=IT.

The hologram records R.I.T.

The thick hologram reilluminated by a plane wave R will diffract animage proportional to IT, that is to say, the image of the transparency,provided that I is of the plane wave type, like R.

As in FIG. 2, the modulator 23 of FIG. 3 can be integrated into ascattering function. For example, a layer of scattering material will bedeposited on the face of the modulator located on the side of the layerof photosensitive material.

In the above, the recording of the hologram 21 has been carried out byplacing thereagainst an optical modulator. It is also possible to designa recording system in which the modulator is illuminated by a wave I,which is modulated by the modulator and which supplies a wave O, as isshown in FIG. 4 a. An optical device 80 images the modulator in theplane of the hologram. Moreover, a beam-splitter plate 81 placed in thepath of the wave O makes it possible to transmit a reference wave R tothe photosensitive medium 21. This reference wave interferes with thewave O and makes it possible to record the image supplied by themodulator 23. The rereading of such a hologram requires placing a mirroragainst the support 22 on the side opposite the hologram 21.

FIGS. 4 b and 4 c represent variants of recording systems in which themodulator is not placed against the hologram. As can be seen in FIG. 4b, the modulator 23 is illuminated by the wave I and is projected by theoptic 80, onto the surface of the layer of photosensitive material 21(wave O=IT). Moreover, the layer of photosensitive material isilluminated by a reference wave R incident on this layer from the sideopposite the modulator. The two waves O and R interfere in thephotosensitive layer in order to record a hologram corresponding to thedisplay of the modulator 23. As is known in the prior art, the waves Oand R are preferably coherent.

FIG. 4 c shows the system of FIG. 4 b in which one or more additionallight modulators 27, 28 have been provided. These modulators are notplaced in the same plane as the modulator 23. These modulators will makeit possible to record, in the photosensitive layer of the hologramswhich will not appear in the same plane as the image of the modulator23.

Preferably, the images of the various modulators will be recordedseparately. The image of the modulator 23 will be recorded when themodulators 27 and 28 are transparent or in the absence of thesemodulators. In order to record the image of an additional modulator, 27for example, the modulator 23 will be made transparent (or removed)possibly together with the modulator 28.

It should be noted that the various holograms recorded using the variousmodulators can be recorded using different wavelengths insofar as thenature of the photosensitive layer 21 allows it. These holograms willthen be reread using these various wavelengths.

The variant of FIG. 4 c making it possible to record visible hologramsin different planes is also applicable to the systems of FIGS. 2 and 3by also providing one or more additional modulators on the path of oneof the waves I or R.

These additional modulators will make it possible to display either aspecific motif (logo) or data (a signature for example) of the documentto be secured.

In order to induce a scattering effect and/or aberrations in thehologram, the means inducing the scattering and/or the aberration can beplaced either in the path of the wave O or in the path of the wave R.

FIGS. 5 and 6 show variants of the systems of FIGS. 2 and 3,respectively, in which optical aberrator devices are provided.

Thus, in FIG. 5, an aberrator 25 is positioned, for example, on thereference wave R. An aberrator introduces a local phase φ into the waveR, that is to say, transforms it into R.e^(iφ).

The modulator is also illuminated by R.e^(iφ) and the object wave O is.O=R.e^(iφ)T. The hologram records R.R. e^(2iφ)T.

In reading mode, illuminated by R, it diffracts a wave e^(2iφ)RTdeformed with respect to RT. The image appears scrambled to theobserver. The observer can read normally only a deformed image. Thedeformation undergone by the image is twice that coming from theaberrator.

If the aberrator 25 is located on the modulator side with respect to thelayer of photosensitive material, the hologram records R.R.T.e^(iφ).This case is similar to the case of recording 2 waves treated below.

In FIG. 6, the system is illuminated by two distinct waves I and Rsupplied by sources S1 and S2 as in FIG. 3.

The aberrator is positioned, for example, in the path of the wave R. Theaberrator introduces a local phase φ into the wave R, that is to say,transforms it into R.e^(iφ).

The transparency is illuminated by a plane wave I. We therefore haveO≠IT.

The hologram records R.e^(iφ) IT.

In reading mode, reilluminated by R, it diffracts a wave e^(iφ) ITdeformed with respect to IT. The image appears scrambled to theobserver, as above.

The deformation undergone by the image is the same as that coming fromthe aberrator.

Under these conditions, in order to be able to reread the imagesrecorded using the systems of FIGS. 5 and 6, it is necessary to correctthe aberrations introduced by the aberrator.

For this purpose, according to the invention, an aberration-correctingdevice 27, which we will call a revealer 27, is placed (FIG. 7) in frontof the hologram thus recorded, through which it is possible to read thehologram corrected of the aberrations.

The revealer induces a phase function the inverse of that of theaberrator, that is e-^(iφ), on the read wave.

The wave incident on the hologram is Re-^(iφ). Since the hologram hasrecorded R.Re^(2iφ)T, it diffracts a wave proportional to T.e^(iφ) thenpasses back through the revealer which again induces e^(−iφ) and thusthe light wave coming from the revealer is proportional to T, that is tosay corresponds to the undeformed image.

Therefore, with a recording such as that of FIG. 6, (aberrator on thereference wave side), the aberrator induces φ, the revealer must induce−φ.

Where the aberrator has been positioned on the modulator side, therevealer is determined as in the two-wave case described below.

According to FIG. 8, the revealer induces a phase function of e^(−iφ) ITon the read wave.

The wave incident on the hologram is R.e^(iφ/2). Since the hologram hasrecorded Re^(iφ)T, it diffracts a wave proportional to T.e^(iφ/2) thenpasses back through the revealer which again induces e^(−iφ/2) and thusthe light wave coming from the revealer is proportional to IT, that isto say it corresponds to the undeformed image.

Therefore with 2 wave recording: the aberrator induces φ and therevealer must induce −φ/2.

In order that the positioning of the revealer is not too critical, theaberrator must be chosen so as to noticeably modify the view of theimage but with phase defect spatial frequencies on the scale of thepositioning accuracy tolerated.

1°/ 1 or 2 wave recording can be carried out with any incident waves.The benefit is, inter alia, to separate the direction of observing therecorded image from the specular reflection. This configurationsubstantially improves the image contrast.

2°/ In FIG. 2, a nonspecular mirror can be used in recording so as tomodify the angle of incidence of the object wave with respect to that ofthe reference wave, namely to separate the direction of observing thephoto from the specular reflection.

3°/ The aberrator and the revealer are two different phase functions. Itis possible to use the same component for both functions byreilluminating the hologram not with R but with R*. In this case, thephase function recorded in the hologram is transformed into itsconjugate by diffraction and self-corrects by passing through this samephase law. This is the principle of phase conjugation.

A hologram of this sort is thus made difficult to counterfeit by thepresence of the aberrator during recording:

-   -   knowledge of the correct aberration function to be used is not        easy to acquire. This analysis can be made difficult by        superimposing a scattering function on the diffracted function;    -   on the assumption that the aberrant function to be used during        recording has been determined, the practical construction of a        known phase law aberrator is not easy.

FIG. 9 shows a device for reading a document furnished with a hologramrecorded with aberrations. This device comprises a revealer 27 whichmust be accurately positioned with respect to the hologram in order toallow sufficient correction of the aberrations. According to FIG. 8, thedocument which bears the hologram or the hologram support comprisespositioning means such as notches 30 to 33. The read device compriseslugs or pads 40 to 43, the complement of the notches, so that thedocument is placed correctly in front of the revealer.

According to a variant embodiment (FIG. 10), instead of notches, thedocument may comprise optical marks 34 to 37 visible through the readdevice 27. The latter also comprises optical marks 44 to 47. Making themarks 34 to 37 coincide with the marks 44 to 47 enables the hologram tobe placed correctly in front of the revealer 27.

To improve the protection against counterfeiting, it is proposed to usea variant of the photosensitive protection of a volume which consists ofthe superposition of several photosensitive functions, one of whichcontains the photo-type personalized data.

By way of example, the following combination is proposed:

-   -   a photo-type hologram (HP) operating in reflection providing the        personalization;    -   a grating-type coding function (HS) operating in transmission        providing the security;

In the case which is described in FIG. 11 illustrating this principle,the function (HP) has been recorded in the holographic layer 21 with anobject wave obtained with the modulator 23 by means similar to theLipmann process and with a reference wave which is the sum of the wavetransmitted by the component HS. In FIG. 11, the component HS is, forexample, a diffraction gating supplying two waves A*_(S.R) and alsoA_(S.O).

To be visible, the photo contained in the component 21 requires thepresence of the coding function of the component HS.

The grating function HS may simply be of the grating type with a fixedpitch or contain specific but not personalized data; it will thereforebe identical for all the cards.

The benefit of the HS coding function resides in the fact that it endowsthe personalized hologram with specific optical properties colorimetry,multiple angular ranges of visibility as a function, for example, of thegrating order number, etc.

The combination of the two components, photosensitive layer and gratingHS (FIG. 12) by “anti-peel” bonding means does not enable the twooptical functions to be separated and consequently makes counterfeitingcomplex insofar as it requires knowledge of the amplitude and phase dataof each of the reference and object waves for each of the two componentsto be recorded. Analysis of the wave diffracted by the assembly givesaccess to a product of all these complex waves;

-   -   if A_(S.R) and A_(S.O) are the reference and object recording        waves, respectively, of the grating HS and A_(l) the wave        incident on HS to record the component 21, then the recording        waves of the hologram 21 are        [A_(S.R.)A_(S.O)+A*_(5.R.)A_(5.O)]A_(l) and A_(P.O).

The image recorded in the hologram 21 will be observed withoutdistortion if the whole (21+HS) is illuminated by the wave A_(l).

Outside these observation conditions, the holographic image will changecolor with the appearance of distortions or will disappear depending onits geometrical characteristics (thickness and index variation), asimple Lipmann hologram does not show such distortions.

According to a variant of the system of FIG. 11, the safety function maycontain data which will be highlighted by the continuous componentreflected by the photosensitive component. To increase the visibility ofthe data reread by the continuous component, it is possible to add, onthe rear face of the hologram, a high index treatment or a treatmentwith narrow spectral reflectivity.

The relative positions of the hologram functions and of the grating HScan be exchanged as well as their kind and type of transmission orreflection.

Where transmission functions are combined, it is possible to add a highindex treatment or a narrow spectral bend reflector (which may or maynot be photosensitive) to increase the readability of the data.

It should be noted that in the above, the photosensitive functions maybe monochrome, dichrome or trichrome, etc., it is possible to adjust thecolorimetry of the image for authentication with a given light source(natural, neon or other light) or code the data stored in one end andthe same layer in different colors.

The use of photosensitive material with swelling that can be spatiallycontrolled by post-treatment makes it possible either to color-code agiven motif superimposed on the personalized hologram, or to includeanother high-resolution function which can be seen with an additionalsource.

In addition, the hologram may be transparent to allow the reading ofdata located under the hologram, on the document.

The hologram can be read either by natural light, or by normalillumination, or using a lamp with a particular range of wavelengths.

It will generally be recalled that:

-   -   if the hologram is thick, it only diffracts the recorded image        with light incident at a particular angle (Bragg effect) and        that the recorded image is only visible from a viewing angle        determined with respect to the direction of the incident light;    -   the illuminating waves R and O are preferably plane but that is        not compulsory;    -   the illuminating waves R and O may be counterpropagating but        that is not compulsory;    -   the illuminating waves R and O are preferably mutually coherent;    -   the hologram can be recorded with a single wavelength or by        using several wavelengths, or else by using three wavelengths        (red, green, blue) so as to diffract white light.

1. A document security system, comprising: a layer of photosensitivematerial; an optical modulator including an image of at least part of adocument and positioned near or in contact with said layer ofphotosensitive material, said image of at least part of the document onthe optical modulator being prerecorded or formed thereon by electricalcontrol of an electrically controllable modulator; an optical devicepositioned between the optical modulator and the layer of photosensitivematerial and configured to image the image of at least part of thedocument of the optical modulator in a plane of the layer ofphotosensitive material; a beam-splitter plate; a first light sourceconfigured to emit a first wave to the beam-splitter plate, saidbeam-splitter plate retransmitting the first wave to the layer ofphotosensitive material; and a second light source positioned on a sideopposite said layer of photosensitive material with respect to saidoptical modulator and configured to emit a second wave that is coherentwith the first wave toward the optical modulator, said second wave beingmodulated by the image of at least part of the document of the opticalmodulator and the modulated second wave being transmitted to the layerof photosensitive material through the optical device and the beamsplitter plate, said modulated second wave interfering with said firstwave in the layer of photosensitive material to record a hologramincluding the image of at least part of the document.
 2. The system ofclaim 1, further comprising a scrambling device positioned in a path ofthe first wave or in a path of the modulated second wave and configuredto induce scrambling in the hologram recorded in the layer ofphotosensitive material.
 3. The system as claimed in claim 2, whereinthe scrambling device is positioned between the first light source andthe beam-splitter plate.
 4. The system as claimed in claim 2, whereinthe scrambling device is positioned between the optical modulator andthe layer of photosensitive material.
 5. The system as claimed in claim4, wherein said scrambling device is positioned at least substantiallyagainst the layer of photosensitive material.
 6. The ssytem as claimedin claim 1, wherein the modulated second wave is perpendicular to theplane of the layer of photosensitive material.
 7. The system as claimedin claim 1, wherein the first wave is perpendicular to the plane of thelayer of photosensitive material.
 8. The ssytem as claimed in claim 1,further comprising a spatial light modulator positioned in a differentplane than that of said optical modulator and configured to record, inthe hologram, an additional image in a plane different from the image ofat least part of the document.
 9. The system as claimed in claim 8,wherein the additional image and the image of at least part of thedocument are recorded at one of different wavelengths or differentangles of incidence of the first wave and the modulated second wave. 10.The system as claimed in claim 1, wherein the first wave and themodulated second wave are plane, coherent, and collinear waves.